The objective of the present study was to determine anti-proteinuric effect of an N-type calcium channel blocker-cilnidipine. Subjects were 43 essential or renal hypertensive subjects who had been taking calcium channel blockers other than cilnidipine for at least 6 months. All patients had proteinuria greater than 0.2 g/day in spite of fair blood pressure control (<150/90 mmHg). Calcium channel blockers in 25 patients (62+/-3 years) were switched to cilnidipine (cilnidipine group), whereas other 18 patients (58+/-3 years) continued to take originally prescribed calcium channel blockers (control group). The 24-hr urine collections were done at baseline and after 6 months of the follow-up period. Baseline characteristics including age, blood pressure levels, body mass index and creatinine clearance were similar between cilnidipine and control groups. Urinary protein excretion also was comparable between cilnidipine (0.61+/-0.10 g/day) and control (0.86+/-0.17 g/day) groups. Urinary protein significantly decreased after 6 months in cilnidipine group (- 0.21+/- 0.11 g/day, - 36%, p< 0.01), whereas it did not change in control group (+ 0.01+/- 0.15 g/day, 0.4%, ns). There were no significant changes in blood pressure, serum creatinine, creatinine clearance, estimated protein intake, and urinary salt excretion during the follow-up period in either group. The reduction of urinary protein by cilnidipine was evident in essential hypertensives (- 54+/-9%, n=18, p<0.01) but not in renal hypertensives (+10+/-35%, n=7, ns). Results suggest that cilnidipine has an anti-proteinuric effect especially in patients with essential hypertension.